SMTP, which stands for Simple Mail Transfer Protocol, is the software that allows you to send out emails from your email addresses. Without this, you won't be able to employ e-mail apps or webmail. When you send an email, your SMTP server creates a connection to a DNS server to learn where the e-mails for the recipient domain name are taken care of. Subsequently, it creates a connection to the remote mail server and exchanges details. When the recipient mail box is available, your server sends the email to the receiving POP/IMAP server and the latter brings that e-mail to the specific mailbox where the recipient can access it. If you'd like to send e-mails, you should always make certain that the hosting company has the service with their plans. Even if you use an online form that website visitors use to contact you, you will still require an active SMTP server for your hosting account for the form to operate.